1. Field of the Invention
The invention relates to a method of and apparatus for handling articles and, more particularly, stacking glass sheets.
2. Discussion of the Prior Art and Technical Problems
The prior art teaches various techniques and equipment for handling articles e.g. sheets. Typical article handling and stacking apparatuses are taught in
______________________________________ U.S. Pat. Nos. U.S. Pat. Nos. ______________________________________ 3,008,747 3,445,313 3,377,223 3,480,160 3,395,915 3,907,127 3,431,010 3,970,341 ______________________________________
In general, U.S. Pat. Nos. 3,008,747; 3,431,010 and 3,970,341 teach pulling a vacuum through cups and/or cylinders to secure sheet thereto. The drawback with using vacuum cups and/or cylinders of the type taught in the above-mentioned patents for handling or stacking sheets is that the procedure is slow because only one sheet can be handled at a time.
U.S. Pat. Nos. 3,377,223; 3,445,313; 3,480,160; and 3,907,127 teach vacuum conveyors for handling and/or stacking sheets. In general, a vacuum is pulled through an endless porous belt to maintain the sheet against the belt. As the belt moves, the sheet is displaced along a sheet movement path toward a release or stacking position. When the sheet is in a predetermined position relative to the release position the vacuum is broken to release the sheet either by urging the sheet away from the belt or shutting off the vacuum. A limitation with the above type apparatuses is that the sheet must be released from the belt when the sheet is in the predetermined release position. For example, when the sheet is released from the belt and moves along a trajectory path into the stacking position, a quick release can result in the sheet falling short of the stacking position and a late release can result in the sheet passing over the stacking position. When the stacking apparatus is of the type having the leading edge of the sheet moving into a stop and thereafter the sheet is released, a late release can damage the sheet because the belt urges the sheet forward but the stop prevents movement of the sheet. An additional problem with a late release is that the belt moves over the surface of the stationary sheet marring same. An early release can result in a non-uniform sheet stack which is difficult to secure for handling.
U.S. Pat. No. 3,395,915 teaches a sheet handling device having a plurality of spaced moving belts moving over a perforated plate. A vacuum is pulled through the plate between the belts to urge the sheet against the moving belts. Although the apparatus eliminates the problem of marring the sheet surface when the sheet engages a stop, there are no provisions for providing a uniform stack of sheets. For example, as the sheet is released, an air cushion between the recently released sheet and stack allows the sheet to freely move sideways, forward and backwards resulting in a non-uniform stack. Providing aligning members to align the stacked sheet e.g. as taught in U.S. Pat. No. 3,907,127 compensates for but does not solve the non-alignment problem.
It would be advantageous therefore to provide a method of and apparatus for handling and stacking sheets that does not have the drawback of the prior art.